1. [Field of the Invention]
The present invention relates to a light emitting device.
2. [Description of the Related Art]
Light emitting device, developed aiming at realizing high-luminance-type ones which use AlGalnP, InAlGaN or the like as a basic material, have been becoming more closer to the theoretical limit of photo-electric conversion efficiency inside the device, as a result of advancement made in the materials and device structures over years. Light extraction efficiency from the device will therefore be a matter of great importance in view of obtaining devices of still higher luminance. One exemplary method generally adopted to obtain a higher light extraction efficiency relates to molding around a device chip using a high-refractive-index resin. More specifically, one widely known light emitting device has a device chip covered with an epoxy resin, as described in Japanese Laid-Open Patent Publication “Tokkaihei” No. 11-191641. The device chip in this case uses the bottom thereof as an emission operation end, so that it is often to adopt a configuration in which the bottom is adhered to a metal stage while placing a electro-conductive adhesive layer such as an Ag paste layer in between, so as to allow application of operation voltage for emission to the device chip, through an operation terminal provided on the metal stage. In this configuration, the device chip adhered onto the metal stage is molded together with the electro-conductive adhesive layer.
For the case where the device chip is resin-molded, most resins expand as being affected by temperature rise during emission operation, day-and-night temperature difference in an environment of use, direct irradiation by sunray in midsummer, and so forth. Any expansion-induced stress applied to the device chip may result in separation of the device chip adhered on the metal stage, and in conduction failure with the metal stage. In particular for the case shown in FIG. 8 of Japanese Laid-Open Patent Publication “Tokkaihei” No. 6-296040, wherein a portion of a GaAs substrate, previously used for allowing the light emitting layer portion to grow thereon, is left unremoved on the bottom side of the device chip so as to allow adhesion on the bottom of the GaAs substrate, a problem arises in that a gap is formed between the light emitting layer portion and the metal stage, in a region where the GaAs substrate has been removed. The above-described expansion of the resin filled in such gap may result in a nonconformity such that the device chip floats as if being jacked up due to displacement caused by the resin expansion, separates from the adhesive layer, and results in illumination failure.
It is therefore an object of the present invention to provide a light emitting device having a structure less causative of separation of the device chip adhered on the metal stage even if the molding resin expands.